Abstract

This thesis is organized around the theme of modulation of transcriptional states in Arabidopsis thaliana. The two particular mechanisms on which this work focuses are (1) microRNA-mediated negative regulation of protein levels (either by mRNA cleavage or by repression of translation) and (2) transduction of extracellular signals into the cell to affect the transcription program.

Chapter 2 characterizes the role of the EARLY EXTRA PETALS (EEP1) microRNA in the regulation of organ formation in the flower and shoot. The eep1 loss-of-function mutant has extra petals, and it enhances the shoot phenotype of the pinoid mutant, which has defects in auxin signaling and organ formation. EEP1 is nearly identical to a pair of published miRNAs (MIR164a and b); all three are predicted to target the mRNAs of six genes in the NAC family of transcription factors. Two of these genes, CUPSHAPED COTYLEDONS1 and 2 (CUC1 and 2), are redundantly required in flower development. Phenotypic and molecular analysis of lines overexpressing EEP1 are consistent with (1) negative regulation of CUC1 and CUC2 by EEP1 and (2) cleavage of the CUC2 mRNA promoted by EEP1.

Chapter 3 describes the investigation, by reverse genetics, of five proteins encoded by genes in the CLV3/ERS (CLE) family. Due to the similarity of these proteins to CLAVATA3 (CLV3), the likely secreted ligand for the CLAVATA1 receptor-like kinase, functional analyses were performed in order to determine whether these proteins might also function as ligands for CLV1 or other receptor-like kinases. The results presented here derive from experiments using overexpression, double-stranded RNA interference (dsRNAi), and promoter-glucuronidase (GUS) reporter expression.